Cases of the West Nile virus have also been reported in 2018 in Hungary, Italy, Romania, and Serbia, according to data from the European Centre for Disease Prevention and Control.
All four cases, the CDC says, were confirmed following blood donations.
People who contract West Nile virus may show mild signs of illness including fever, headache and body aches.
Brenda Miller is the manager of health protection and investigation with Region of Waterloo Public Health and said the region monitors 16 different sites for West Nile virus in recreational and residential areas.
Health officials said that doesn't automatically mean there's cause for alarm.
This year, West Nile has not yet been found in a Wisconsin resident.
Health officials say that most people infected with the virus do not see any symptoms.
The Cape Cod Times reports that state Department of Health said Thursday 14 mosquito samples from Falmouth, Barnstable, Dennis, Bourne and Yarmouth tested positive for the virus after being trapped Tuesday and July 31.
People of any age can become sick from the virus but those aged 50 and above, or who have weak immune systems, have the highest risk, according to the World Health Organization.
Experts recommend using insect repellent, avoiding the peak mosquito feeding times of dawn and dusk and wearing loose fitting clothing.